This invention relates generally to high pressure pipes, and more particularly to fittings to connect pipes to valve bodies.
A fitting connects a pipe to a body, e.g., a valve assembly. The fitting also acts as a seal so that the material in the pipe/body does not escape into the environment.
Hydrogen storage systems are being developed for automotive applications. These storage systems have several important sealing requirements, which are challenging because of the hydrogen molecule's small size. The fitting has to operate under high pressure conditions, e.g., up to about 875 bar (87.5 MPa). It also has to operate at low temperatures, e.g., down to about −40° C., as well as at temperatures up to about 85° C. Because the fitting will be mounted under the body of the vehicle, it will be exposed to corrosive materials. In addition, the fitting should be able to be opened and closed several times. It also should be able to operate when the pipe and valve body are made of different materials, e.g., when the pipe is made of stainless steel and the valve body is made of aluminum.
WO 2009/100898 A1 describes one type of fitting for a valve assembly. There is a valve body 10. A pipe 15 is connected to the valve body 10. There is a seal case 20 attached to the pipe 15 by weld 25. The seal case 20 forms a flange around the pipe 15 that supports seal 42. The nut 30 fits into the valve body 10. The nut 30 is on the low pressure side of the flange. There is a retaining washer 35 between the nut 30 and the seal case 20. The seal 42 between the valve body 10 and the seal case 20 is provided by a solid ring made of poly ether ether ketone (PEEK). For low temperature applications, seals made of most elastomers are not suitable because they become hard and brittle, and plastic materials such as PEEK have to be used. However, plastic materials have limited elasticity, leading to the danger of increased leaks at temperatures below −40° C. In addition, the contact area at the body is conical, making it difficult to keep tight tolerances.
Therefore, it would be desirable to have a fitting which provides a good seal for hydrogen, including at low temperatures.